Problem: The sum of two numbers is $21$, and their difference is $1$. What are the two numbers?
Answer: Let $x$ be the first number, and let $y$ be the second number. The system of equations is: ${x+y = 21}$ ${x-y = 1}$ Solve for $x$ and $y$ using elimination. Add the top and bottom equations together. $ 2x = 22 $ $ x = \dfrac{22}{2} $ ${x = 11}$ Now that you know ${x = 11}$ , plug it back into $ {x+y = 21}$ to find $y$ ${(11)}{ + y = 21}$ ${y = 10}$ You can also plug ${x = 11}$ into $ {x-y = 1}$ and get the same answer for $y$ ${(11)}{ - y = 1}$ ${y = 10}$ Therefore, the larger number is $11$, and the smaller number is $10$.